Association Between Gender and Payments Received From Pharmaceutical Companies Among Medical Professors and Associate Professors in Japan

Introduction While prior research showed gender gaps in industry payments for medical professionals in the United States, there are limited data in Japan. So, this study seeks to investigate the potential gender gap in the receipt of pharmaceutical companies (PFCs) across all medical fields in Japan. Based on the results of previous studies, we developed a hypothesis that male doctors get more PFC than female doctors. Materials and methods Data from 92 pharmaceutical companies in Japan, covering 2016 to 2019, were analyzed. The analysis was conducted on professors and associate professors at all national and public medical universities in Japan, with gender as a factor variable and payments as an outcome variable, and variables that may have influenced the factor or outcome variables in previous studies, such as specialization, university type, region, rank and years since graduation, as control variables. Payments were converted to US dollars using the December 31, 2021, rate of 115 yen to the dollar for comparison purposes. Results Out of 1,825 subjects, 1,755 were males and 70 females. Males consistently received higher median payments from pharmaceutical companies (PFCs) than females across categories. In particular, among physicians specializing in internal medicine, the median PFC for men was $25 compared to $8 for women. For physicians affiliated with former imperial universities (the seven former imperial universities founded before World War II), the median PFC for men was $32 compared to $5 for women. Multivariate analysis confirmed significantly higher total benefits for males from 2016 to 2019, with the gender gap widening during this period (incidence rate ratio (IRR) for 2016: 0.51, IRR for 2019: 0.44). Conclusions Japanese male professors and associate professors received significantly higher PFCs than their female counterparts, and this gender gap expanded from 2016 to 2019, highlighting persistent gender inequality in the medical field in Japan, similar to trends observed in the United States.


Introduction
Payments from industry play a significant role in medical research and clinical care [1][2][3].For example, according to Boddapati et al., those receiving more than $100,000 per year from the industry had significantly more publications and a higher h-index for publication quality than those receiving less than $10,000 per year for all positions [2].However, the receipt of money from industry, especially from pharmaceutical companies, also carries the risk of overprescribing expensive drugs [4][5][6].Indeed, Inoue et al. investigated the association between industry payments to physicians and long-acting insulin prescribing behavior [4].Specifically, the results showed that physicians who received industry payments prescribed $22,111 more long-acting insulin than those who did not [4].
Several factors that determine the amount of payment from pharmaceutical company (PFC) have been investigated, for example, job position, age, department of practice, etc. [7][8][9].Also, gender is one of the factors.For instance, a previous study reported that among rheumatologists in the US, men received only $639 more in industry payments than women [7].Moreover, a study examining pharmaceutical company funding among psychiatrists using the Centers for Medicare and Medicaid Services' Sunshine Act Open Payment database and the 2021 National Plan and Provider Enumeration System (NPPES) database found that women receive approximately 80% of the funding from pharmaceutical industry companies as men do [10].
However, a comprehensive survey covering all medical specialties has not yet been conducted on this topic in Japan.Japan has one of the lowest percentages of female physicians among the Organization for Economic Co-operation and Development (OECD) countries, so the difference in PFC is expected to be even larger due to the large gender gap [11].Therefore, this study seeks to investigate the potential gender gap in the receipt of PFC across all medical fields in Japan.Based on the results of previous studies, we constructed the hypothesis that men obtain more PFC than women.

Study participants
We compiled payment data for lectures, writing and consulting from 92 pharmaceutical companies that disclosed payment data according to Japan Pharmaceutical Manufacturers Association (JPMA) guidelines for Japanese university medical schools from 2016 to 2019 [12].Payment items such as meals, travel and lodging were excluded from the tabulation because they were disclosed in aggregate amounts.In this study, we focused specifically on professors and associate professors because prior research suggested that there may be disparities in the amount of PFC received by degree [13].To complement this data, relevant subject information was collected from online sources and integrated into the database.Due to the unique regulations governing faculty members at private universities, this study included 42 national universities, eight public universities and the National Defense Medical College.

Dependent, independent and control variables
We employed gender as the independent variable and PFC as the dependent variable.We converted the PFC amounts to US dollars using an exchange rate of 115 yen to the dollar as of December 31, 2021.In addition, several variables that influence exposure factors or outcomes were employed as confounding factors with reference to previous study [14].Specifically, we incorporated as control variables the department of specialty, the governing body of the affiliated university, the location of the affiliated university, job rank and the number of years since graduation as factors that may affect PFC in reference to previous studies [8,9,13,15,16].

Statistical analysis
We calculated summary statistics by gender for the variables collected as independent, dependent and control variables.We also calculated the median for each category of each variable by gender and compared whether there were differences between genders.In addition, to assess gender-based differences in PFC from 2016 to 2019, as well as for each individual year within that period, we applied a negative binomial distribution model to analyze the payments received by the individuals in our study.The significance level was set at 5% two-sided, and R statistical software (version 4.3.0,R Project for Statistical Computing, Vienna, Austria) was used for analysis [17].

Ethical approval
The Ethics Committee of the Medical Governance Research Institute approved the study (approval number: MG2018-04-20200605; approval date: June 5, 2020).Informed consent was waived due to this being a retrospective study that used publicly available data.

Results
Study participants with one or more missing values in the items of the collected variables were excluded from the analysis, assuming that the missing values were randomly present.The final analysis included 1,825 subjects (1,755 males and 70 females).Table 1 shows the characteristics of the analyzed population by gender.Most of the population was male, and the median PFC was significantly higher for males; the specialty was mostly internal medicine for both males and females, and the operating organization of the institution where the population belonged to was mostly other public universities.Most of the population in the analysis were in non-professor positions, and most of the male and female population had graduated from 11 to 20 years.

Characteristics of the analyzed population
Total n = 1,825 1  Male n = 1,755 Table 2 shows the median for each attribute by gender.The median was significantly higher for men in most attributes, especially for those from former imperial universities (median (Q1, Q3): $32,000 ($9,000, $93,000) vs. $5,000 ($1,000, $29,000)).When looking at the medians calculated for each variable's category, significant differences between men and women existed in most categories, but there were no significant differences between men and women in the median PFC for those specializing in surgery; those belonging to universities in the Kinki, Kyushu and Okinawa regions; and those in the position of professor.The results of the multivariate analysis are presented in Table 3.The multivariate analysis reveals that even after adjusting for potential confounding factors, the total amount received was still significantly higher for men from 2016 to 2019 (incidence rate ratio (IRR): 0.41, 95% confidence interval (95% CI): 0.